The treatment of textiles with various substances in order to change the properties thereof is well known. For example, it is known that textiles may be waterproofed by coating them with natural or synthetic rubber. Substances have been developed which when sprayed onto fabrics introduce the property of stain resistance. Also known is the example of a fragrance delivery system which uses breakable fragrance-filled microcapsules which are attached to the surface of a fabric or fiber and upon the introduction of an external force, the microcapsules break releasing the fragrance over an extended time period.
Other examples of microcapsules being applied to the surface of fabrics for various end-uses are known. U.S. Pat. No. 4,774,133 to Doree et al. discloses a thermoplastic substrate bearing rupturable microcapsules in a binder. The substrate is capable of being softened when heated, and by the application of pressure the microcapsules become partially imbedded in the surface of porous objects such as fabrics. A thermo-adhesive textile product is disclosed in U.S. Pat. No. 4,990,392 and comprises a backing fabric and an adhesive layer deposited on its surface. The adhesive layer comprises a thermo-adhesive polymer and a cross-linking agent which is isolated from the polymer by microencapsulation and which is freed by external action. The present invention differs from the forgoing examples in that the microcapsules contain phase change material and are designed to be an integral and permanent part of a coating applied to a substrate, as opposed to being ruptured during use.
Fabrics have been given enhanced thermal properties by coating the fibers with phase change material and plastic crystals. U.S. Pat. No. 4,871,615 discloses temperature adaptable textile fibers which store heat when the temperature rises and release heat when the temperature decreases, in which phase change or plastic crystalline materials are enclosed within hollow fibers, or impregnated upon non-hollow fibers. The fibers are produced by dissolving the phase change or plastic crystalline materials in a solvent such as water, thereafter filling the hollow fibers, or impregnating the non-hollow fibers, with the solution, followed by removal of the solvent. Alternatively, the phase change materials may be applied to the fibers from a melt rather than a solution.
At the phase change temperature, a characteristic of phase change material during the heating cycle is to absorb and hold a quantity of thermal energy at almost a constant temperature while changing to the next phase. Thus, the material can be precooled and used as a barrier to heat, since a quantity of thermal energy must be absorbed by the phase change material before its temperature can rise. The phase change material may also be preheated and used as a barrier to cold, as a quantity of heat must be removed from the phase change material before its temperature can begin to drop.
However, the durability of the aforementioned surface mounted phase change materials was found to be lacking. While somewhat effective, the fabric lacked repeatability of the thermal response. Each successive laundering removed a portion of the phase change material, thus causing the fabric to exhibit a corresponding change in thermal properties which limited its usefulness and lifetime. As a result, further work was undertaken to perfect a series of process steps for binding the phase change material to the fabric in order to extend the useful life of the enhanced thermal properties. Furthermore, as far as is known to the inventors, these fibers and fabrics have limited usefulness as only a single phase change material may be applied to the substrate which requires that the thermal absorption or release occur at a specific temperature.
It is, therefore, an object of the present invention to provide a substrate coating with enhanced thermal retention properties.
It is another object of the present invention to provide a substrate coating which will maintain its enhanced thermal properties over an extended period of time.
It is another object of the invention to provide a substrate coating having enhanced thermal properties which can be produced with a minimum of process steps.
It is a still further object of the present invention to provide a substrate coating having enhanced thermal properties which can be applied to a fabric from which articles of clothing and the like can be manufactured.
It is a still further object of the present invention to provide a substrate coating which displays enhanced thermal properties over a specified temperature range.
A related object of the present invention is to provide a thermal control material having enhanced thermal storage properties that are reversible.